Keep an Eye of the Deep on Aquatic Adventures in D&D

Sometimes, adventures in fifth edition Dungeons & Dragons take you away from dry land and the comfort of familiar tropes. When ancient evil threatens the world from the ocean floor, when rumors of a sunken city offer the prospects of rewards untouched by man, or simply when a transport ship sinks, then its time to dive below the waves. Aquatic adventures in D&D can offer a fresh new experience for players and give the Dungeon Master an opportunity to play with some creatures and locations that tend to go untouched. So, strap on your swim cap as we dive into running an adventure underwater.

Sahuagin are one of the terrors of the deep in D&D. Here, adventurers go toe-to-webbed-toe with one of the sea devils and its hammerhead shark steed. [Art by Craig J. Spearing]

Aquatic environments

Running an underwater D&D game will allow you to use a bunch of cool new encounter locations. An underwater environment could be a sunken ruin, or a vast aquatic wilderness dotted with unique landmarks. This is your opportunity to throw something completely unique at the players, or to put a unique spin on a trope that is normally found on dry land.

The wreck of a sunken treasure ship

A massive bed of oysters hidden in an aquatic crevasse

A chromatic coral reef swimming with colorful fish

The lava tube of an underwater volcano

Ancient stone ruins of a once-great city

A forest of swaying kelp that rises to the water’s surface

Inside a floating iceberg

In the belly of a sea monster

[NERDITOR’S NOTE: You can head over to Adventure Lookup to search for more aquatic adventures in D&D — just don’t expect to see an underwater D&D game set in a giant clam.]

Aquatic creatures for your underwater D&D game

There are a lot of interesting creatures in the Monster Manual that seem to just sit and collect dust. Truthfully when was the last time you fought a giant shark? Infiltrated a sahuagin baron’s estate? Explored an ancient city full of chuul, only to encounter a sleeping aboleth? Maybe you have fought a lich before, but have you fought one at the ocean’s floor, in a castle carved from the bones of a kraken? Aquatic campaigns are an opportunity to pull some of the lesser-known creatures from the Monster Manual, as well as the perfect way to put a unique spin on some undead and constructs who don’t need to breathe. If you’re ambitious, older versions of D&D offered many aquatic creatures that haven’t been launched yet that you can draw inspiration from. Create an updated version of an old creature to really keep the players on their toes. Here is an example of an Eye of the Deep I made for one of my upcoming adventure books.

Blinding Gaze. When a creature that can see the eye of the deep’s central eye starts its turn within 30 feet of the eye of the deep, the eye of the deep can force it to make a DC 14 Constitution saving throw if the eye of the deep isn’t incapacitated and can see the creature. A creature that fails the save is blinded. A blinded creature may repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Unless surprised, a creature can avert its eyes at the start of its turn to avoid the saving throw. If the creature does so, it can’t see the eye of the deep until the start of its next turn, when it can avert its eyes again. If the creatures looks at the eye of the deep in the meantime, it must immediately make the save.

Water Breathing.The eye of the deep can breathe only underwater.

ACTIONS

Multiattack. The eye of the deep can make two attacks, one with its bite and one with its claws.Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target hit 9 (2d8 piercing damage)Claw.Melee Weapon Attack: +6 to hit, reach 5 ft., one target hit 5 (1d6 +2 bludgeoning damage, and the target is grappled (escape DC 14). The eye of the deep has two claws, each of which can grapple only one target.Eye Rays. The eye of the deep chooses one of the following magical eye rays to use as an action. The eye rays have a maximum range of 60 feet.

Right Paralyzing Ray. The targeted creature must succeed on a DC 14 Wisdom saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Left Paralyzing Ray. The targeted creature must succeed on a DC 14 Wisdom saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Combined Eye Rays. The eye of the deep produces the effects of the silent image spell requiring no spell slot, components, or concentration.

Tactics in your underwater D&D game

Any aquatic adventures in D&D that include some amount of underwater exploration are an opportunity to try some fun new combat tactics. Now, battles happen in three dimensions with all the characters able to swim up and down and fight at various depths and from different angles. Suddenly, the possibility of unique spell combinations ignites the imaginations of DMs and players alike. However, the rules in fifth edition D&D regarding underwater combat are somewhat vague and leave a lot to be handled on a case by case basis. We do get a bit about submerged creatures having resistance to fire, but what about lightning, acid, thunder and cold? That kind of stuff can of course turn into an entrenched rules debate that lasts an unsettling amount of time. To maximize the fun and keep the action going, you probably want to talk this out with your group prior to the start of the game and establish some of the most common situations that may arise. Do submerged creatures have vulnerability to lightning? Advantage on saves against acid? In an underwater adventure many of these questions are going to arise constantly, so it’s best to give it a bit of thought well in advance to starting the game. The amount of fiddling with the rules you want to do may vary on a group by group basis. In most cases the easiest thing to do when an absolutely obscure “depth pressure vs thunder damage” question arises on the fly is just hand wave it so that works as it always does, or it functions in a way that is the most fun and interesting for the story.

Jumping into an aquatic adventures in D&D

Once you’ve nailed your locations, encounters, and rules you are ready to take the dive into an underwater adventure. If you want to run an aquatic adventure but still feel a bit overwhelmed, the Tides of Fate series is available on DMs Guild. Tides of Fate is a modular campaign for first tier character that starts at first level and ends at fifth level. It’s a fantastic way to let new DMs and players dip their toes in the water without immediately throwing them in the deep end. [NERDITOR’S NOTE: You can use Nerdarchy’s exclusive coupon code DTRPG-Nerdarchy for a one-time 10 percent discount on orders of digital products $10 or more, good at DM’s Guild or any of the OneBookShelf sites like DriveThruRPG.]

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